Many of the medical care garments and products, protective wear garments, mortuary and veterinary products, and personal care products in use today are partially or wholly constructed of nonwoven web materials. Examples of such products include, but are not limited to, medical and health care products such as surgical drapes, gowns and bandages, protective workwear garments such as coveralls and lab coats, and infant, child and adult personal care absorbent products such as diapers, training pants, swimwear, incontinence garments and pads, sanitary napkins, wipes and the like. For these applications nonwoven fibrous webs provide tactile, comfort and aesthetic properties which can approach those of traditional woven or knitted cloth materials. Nonwoven web materials are also widely utilized as filtration media for both liquid and gas or air filtration applications since they can be formed into a filter mesh of fine fibers having a low average pore size suitable for trapping particulate matter while still having a low pressure drop across the mesh.
Nonwoven web materials have a physical structure of individual fibers or filaments which are interlaid in a generally random manner rather than in a regular, identifiable manner as in knitted or woven fabrics. The fibers may be continuous or discontinuous, and are frequently produced from thermoplastic polymer or copolymer resins from the general classes of polyolefins, polyesters and polyamides, as well as numerous other polymers. Blends of polymers or conjugate multicomponent fibers may also be employed. Nonwoven fibrous webs formed by melt extrusion processes such as spunbonding and meltblowing, and formed by dry-laying processes such as carding or air-laying of staple fibers are well known in the art. In addition, nonwoven fabrics may be used in composite materials in conjunction with other nonwoven layers as in a spunbond/meltblown (SM) and spunbond/meltblown/spunbond (SMS) laminate fabrics, and may also be used in combination with thermoplastic films. Nonwoven fabrics may also be bonded, embossed, treated and/or colored to impart various desired properties, depending on end-use application.
Melt extrusion processes for spinning continuous filament yarns and continuous filaments such as spunbond fibers, and for spinning microfibers such as meltblown fibers, and the associated processes for forming nonwoven webs or fabrics therefrom, are well known in the art. Typically, continuous fiber nonwoven webs such as spunbond nonwoven webs are formed with the fiber extrusion apparatus, such as a spinneret, and fiber attenuating apparatus, such as a fiber draw unit (FDU), oriented in the cross-machine direction or “CD”. That is, the apparatus is oriented at a 90 degree angle to the direction of web production. The direction of nonwoven web production is known as the “machine direction” or “MD”. Also, melt extrusion processes as are known in the art for spinning microfibers and making microfiber webs, such as meltblown webs, are generally oriented with the microfiber extrusion apparatus oriented at a 90 degree angle to the direction of web production. Although the fibers are laid on the forming surface in a generally random manner, still, because the fibers generally exit the CD oriented spinneret and FDU in a direction substantially parallel to the MD, the resulting nonwoven webs have an overall average fiber directionality wherein more of the fibers are oriented in the MD than in the CD. Such properties as material tensile strength and web extensibility, for example, are strongly affected by fiber orientation. For example, typical MD:CD tensile strength ratios for continuous fiber nonwoven webs such as spunbond nonwoven webs are generally higher than 1.5:1 and typically 2:1, or even higher. Therefore, it has been difficult to produce nonwoven webs wherein the properties of the material are balanced with respect to the MD and CD material directions.
Consequently, there remains a need for a production process that provides nonwoven webs with improved balance of material properties and of higher overall uniformity than heretofore known.